In recent years, polymer electrolyte fuel cell attracts attention as a source of power of an electric vehicle etc. The solid polymer electrolyte fuel cell (PEFC) can generate electricity at normal temperatures, and is being put in practical use.
Generally, a fuel cell system includes a cathode pole on one side, an anode pole on the other side, and a polymer electrolyte membrane interposed therebetween. This system drives external load with electric power generated by the chemical reaction of oxygen in the air supplied to the cathode pole, and hydrogen supplied to the anode pole.
In a fuel cell system with above arrangement, hydrogen and air must be supplied by more than the amount which a fuel cell consumes, in order to discharge condensation water from the fuel cell which is generated within the fuel cell or to obviate damage of the fuel cell due to a fuel shortage.
By the way, hydrogen is supplied to a fuel cell from a high-pressure hydrogen storage tank such as a cylinder. If the hydrogen which is not consumed is emitted into the atmosphere, this increases hydrogen fuel consumption remarkably. Therefore, a fuel circuit of the fuel cell system adapted to circulate hydrogen by an ejector which is a kind of a hydrogen pump (fuel pump) which performs inhalation and sending by movable portions, such as a rotation mechanism and a rocking part, as shown in FIG. 19 and FIG. 20, or a jet pump is devised.
A fuel circuit of the fuel system is arranged in a below-mentioned manner.
A fuel circuit of the fuel cell system 100 which circulates fuel only with a hydrogen pump decompresses the pressure of the hydrogen discharged from a high-pressure hydrogen storage tank 104 by a regulator 103, as shown in FIG. 19. The decompressed hydrogen is supplied to a fuel cell 101 through a fuel supply stream passage 105. The hydrogen supplied to the fuel cell 101 reacts with oxygen in the air which is supplied to a cathode pole side to cause electricity to be generated in the fuel cell 101. The hydrogen remaining unreacted and existing in the fuel cell 101 is discharged from the fuel cell 101, and is taken in by hydrogen pump 102 provided in a fuel circuit stream passage 106. The unreacted hydrogen which was taken in by the hydrogen pump 102 and sent out is made to be merged with the hydrogen which flows through the hydrogen supply stream passage 105 on a downstream side of the hydrogen pump 102, and recirculated to be supplied to the fuel cell 101.
On the other hand, a fuel circuit of the fuel cell system is also arranged in a below-mentioned manner.
A fuel circuit of the system 200 which circulates fuel only by an ejector decompresses the pressure of the hydrogen discharged from a high-pressure hydrogen storage tank 204 with a regulator 203 as shown in FIG. 20. Then, the decompressed hydrogen is supplied to an ejector 202. The hydrogen thus supplied to the ejector 202 generates negative pressure before being supplied to a fuel cell 201. The hydrogen supplied to the fuel cell 201 reacts with oxygen in ambient-air which is supplied to a cathode pole side to cause electricity to be generated in the fuel cell 201. The existing unreacted hydrogen is discharged from the fuel cell 201, and merged with inhalation mouth 202a which has negative pressure of the ejector 202. The existing unreacted hydrogen which has been merged is mixed and compressed with the hydrogen supplied from the regulator 203 within the ejector 202, and recirculated to fuel cell 201.
However, since the fuel circuit of the fuel cell system 100 with the hydrogen pump 102 circulates hydrogen by the hydrogen pump 102, broad flow rate range needs to be covered by the hydrogen pump 102 only.
This poses a problem of scaling up of the hydrogen pump 102 per se to operate less efficiently. Then, a problem of increasing of power consumption is also involved therein.
Also, in the fuel circuit of the fuel cell system 200 with the ejector 202 only, negative pressure is generated by use of a pressure energy in the high-pressure hydrogen storage tank 204. This negative pressure is used in such a manner that the unreacted hydrogen discharged from the fuel cell 201 is made to be merged with the hydrogen supplied from the regulator 203, and they then subjected to be mixed and compressed therein, and recirculated. Whereas, a problem of wasting pressure energy is involved in the fuel circuit of the fuel cell system 100 with only the hydrogen pump 102.
On the other hand, the fuel circuit of the fuel cell system 200 with the ejector 202 only also poses a problem.
Since a nozzle for transforming pressure energy into speed energy is inserted into the ejector 202, if output of the fuel cell 201 increases rapidly due to acceleration of vehicles, response delay as shown in FIG. 21A arises incurring the problem in which circulation amount does not reach a target value immediately.
On the contrary, when output of fuel cell 201 decreases due to slowdown of vehicles, since hydrogen is not consumed by the fuel cell 201 as shown in FIG. 21B, negative pressure stops being generated in the ejector 202. Therefore, circulation is no longer performed, incurring the problem that circulation amount of the ejector 202 falls immediately.